Method of preparing a color subtractive mask

ABSTRACT

A method of preparing a color subtractive mask for a color matrix to be used for the reproduction of images appearing on a color print, the matrix defining a pattern of identical red, blue and green spot groups similar to that utilized in color television interlace scanning, wherein spot areas of the color print in a pattern corresponding to the matrix spot group pattern are selectively photographed on black and white film through appropriate color filters so that the light exposures of the film spots corresponding to the respective matrix red, blue and green spots are in accordance with the intensities of the respective red, blue and green color components at the corresponding areas of the color print, the relative light intensity information from a resulting matrix size negative being transferred onto a matrix sheet mask to form mask apertures, the size of each aperture being determined by the intensity of the light recorded on the corresponding negative pattern spot.

United States Patent inventor Ramon Bergero Inglewood, Calll. Appl. No. 852,890 Filed Aug. 25, 1969 Patented Sept. 21, 1971 Assignees Gordon Baskin Hollywood, Calif. Jason Tarser Hollywood, Calif.; Attel, Inc., Los Angeles, Calif.

METHOD OF PREPARING A COLOR SUBTRACTIVE MASK J 9 Claims, No Drawings U.S. Cl 96/27, 96/30 Int. Cl G03c 5/04, G03f 7/00 Field of Search 96/30, 27, 45, 1 16, 44

[56] References Cited UNITED STATES PATENTS 2,360,587 10/1944 Sanders 96/30 2,798,428 7/1957 Tollenaar 96/30 X Primary Examiner-J. Travis Brown Assistant Examiner-Alfonso T. Suro Pico Attorney-Spensley and Horn ABSTRACT: A method of preparing a color subtractive mask for a color matrix to be used for the reproduction of images appearing on a color print, the matrix defining a pattern of identical red, blue and green spot groups similar to that utilized in color television interlace scanning, wherein spot areas of the color print in a pattern corresponding to the matrix spot group pattern are selectively photographed on black and white film through appropriate color filters so that the light exposures of the film spots corresponding to the respective matrix red, blue and green spots are in accordance with the intensities of the respective red, blue and green color components at the corresponding areas of the color print, the relative light intensity information from a resulting matrix size negative being transferred onto a matrix sheet mask to form mask apertures, the size of each aperture being determined by the intensity of the light recorded on the corresponding negative pattern spot.

METHOD OF PREPARING A COLOR SUBTRACTIVE MASK CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to the present inventors copending [1.8. Pat. applications Ser. No. 857,277, for a Color Display System, and Ser. No. 862,588, for an Electro-Mechanical Color Reproduction System, both filed concurrently herewith; however, this application is in no way dependent upon the aforesaid copending applications for disclosure support, nor is reference thereto necessary for a full and complete description and understanding of the present invention.

BACKGROUND OF THE INVENTION In the field of large-scale sheet display it has been long customary to print the display information on strips of paper which are then pasted'on a billboard in proper registry with each other to form the display. The advent of electrical and elctro-optical displays has considerably shortened the time and effort required for a display change; yet these newer systems are not without their attendant disadvantages, particularly in color reproduction applications. In such applica tions it has been heretofore customary to either utilize relative expensive electro-optical projection system or a cumbersome matrix screen of many colored light bulbs together with necessary control system for selecting the bulbs to be illuminated. In his above-referenced copending US. Pat. application entitled Color Display System" applicant has disclosed a relatively simple and inexpensive color display system utilizing a color matrix defining a pattern of identical red, blue and green spot groups similar to that utilized in color television interlace scanning, portions of the matrix spots being blackened in accordance with a color subtraction technique to produce a desired colored image display. In his above-referenced copending US Pat. application entitled Electro-Mechanical Color Reproduction System applicant has disclosed a system for preparing the matrix mask in applications wherein it is desired to reproduce images appearing on a color transparency. The present invention is directed toward a method, of preparing the matrix mask in applications wherein it is desiredto reproduce images appearing on a color print.

In both of the above-referenced copending applicationsa color subtraction technique is employed to render opaque, portions of equally sized color spots. In the prior art matrix technique for color reproduction, colored spots of different sizes are formed on an opaque, black background, typically in a three-step process, each step involving the application of a different color. The present invention method is based upon use of the color subtraction technique employed in the referenced copending applications.

SUMMARY OF THE INVENTION The present invention method comprises masking the color print with an opaque sheet mask defining a pattern of apertures corresponding to the matrix red spots and then photographing the so-masked print on black and white film through a filter which selectively passes red light. The print is then masked to expose a pattern of spots corresponding to the matrix blue spots and the so-masked print then photographed through a filter which selectively passes blue light. The print is again masked to expose a pattern of spots corresponding to the matrix green spots and the sb-masked print then photographed through a filter which selectively passes green light. A composite black and white negative, the size of the matrix, is then prepared, the composite negative defining a pattern of three spot groups corresponding to the spot group pattern of the matrix, with the light exposure of the negative spots corresponding to the matrix red spots being in accordance with the intensity of the red color component at the corresponding areas of the color print, the light exposure of the negative spots corresponding to the matrix blue spots being in accordance with the intensity of the blue color component at the corresponding areas of the color print, and the light exposure of the negative spots corresponding the matrix green spots being in accordance with the intensity of the green color component at the corresponding areas of the color spots being in accordance with the intensity of the green color component at the corresponding areas of the color print. The relative light intensity information from the composite black and white negative is then transferred onto a matrix sheet mask in such a manner as to form mask apertures, the size of each aperture being determined by the intensity of the light recorded on the corresponding negative pattern spot. The composite negative can be easily prepared by a triple exposure of the same black and white film frame, the matrix sheet mask being conveniently prepared from the composite negative by a silk screening technique.

The mask is used by placing it in register with the color matrix and applying a black, opaque masking substance to those matrix spot areas remaining exposed through the mask apertures, masking substance application typically being by spraying or painting. Upon removal of the mask the prepared matrix remains, the desired images being reproduced by a color subtraction technique.

Alternatively, the relative light intensity information from the composite negative could be transferred onto a transparent sheet mask in such manner as to form opaque spots thereon, the opaque spot sizes being determined by the intensity of the light recorded on the corresponding negative pattern spots. Both positive and negative masks are envisioned, in accordance with the disclosure of copending application entitled Electro-Mechanical Color Reproduction System, as are all of the various mask applications therein discussed.

The present invention method provides a considerable saving of time, expense and effort over the prior art technique which involves three color applications steps utilizing three separate matrix masks, the present method involving a single color (black) application step utilizing only a single matrix mask. f

DESCRIPTION OF THE PREFERRED EMBODIMENT As hereinabove stated, the present invention method was developed for use in the preparation of a color matrix for the reproduction of images appearing on a color print, the matrix consisting of a repetitive pattern of primary color spot groups similar to that used in color television interlace scanning, each spot group consisting of a red spot and a blue spot and a green spot. In its original state the matrix spots are all the same size, appropriate areas of the spots being blackened in accordance with a color subtraction technique for reproduction of the color images from the print. A typical matrix consists of 260- spot groups arranged in a horizontal line, there being 560 such lines with the spot groups of one line slightly offset from those of the adjacent lines to effect an interlaced spot group pattern, these particular parameters having been found to provide an eye pleasing picture composition. Of course, other matrix parameters can be used without departing from the scope of the invention.

To practice the present invention method, in a first presently preferred embodiment, three sheet masks the size of the color print are prepared, the masks being of an opaque material. The first mask defines a pattern of apertures therethrough corresponding to the pattern of the color matrix red spots, the second mask defining a pattern of apertures therethrough corresponding to the pattern of the matrix blue spots and the third mask defining 'a pattern of apertures therethrough corresponding to the pattern of the matrix green spots.

The first mask is placed on the color print and the somasked print photographed on black and white film through a filter which selectively passes only red light, thereby exposing the film in spot areas corresponding to the matrix red spot pattern, the light intensities of each spot being determined by the intensity of the red color component at the corresponding point on the color print.

The first mask is then replaced by the second mask, the second mask being positioned exactly as the first mask was, the already photographed spot areas of the color print now being masked due to the different aperture locations on the second mask, and the same black and white film frame again exposed, this time through a blue-pass filter. Thus a double exposure results in which the exposed spot areas on the film correspond to the matrix red and blue spot patterns. To insure identical film positioning with respect to the color print the camera and print are mounted on fixed supports.

Then, the second mask is replaced by the third mask, again positioned exactly as the other masks were, and the now double exposed black and white film frame again used to photograph the so-masked color print, now through a green-pass filter. Thus, a triple exposure results to record on the film frame a spot pattern identical to the complete spot pattern of the color matrix, the light intensity at each spot recorded on the film frame being determined by the appropriate primary color component intensity at the corresponding point on the color print.

Next, the film frame is developed and the resulting negative enlarged to the size of the color matrix, to thereby form what can be called a composite negative which, if placed in alignment with the color matrix, would have all of its spots in exact registry with those of the matrix.

The image pattern of the composite negative is then transferred onto a silk screen by shining a strong light through the negative onto the screen, the pores in the silk material being enlarged in direct proportion to the amount of light striking it through the negative, the negative image being literally burned" into the silk.

Finally, the silk screen matrix mask is placed in alignment on the color matrix surface with the spot pattern on the silk screen in registry with the matrix spot pattern and black ink rolled onto the silk screen surface, the amount of ink penetrating through the silk pores being greater in those areas corresponding to white areas of the composite negative. It is a phenomenon of the silk-screening process that the stronger the light exposure on the screen, the larger area that ink will flow through the material pores. Thus, in a spot area wherein a strong color component intensity was recorded on the negative, the negative area would be darker, resulting in less opening of the silk screen pores in that area, and therefore in less masking substance being applied to the matrix surface, and vice versa. In this manner, through use of the silk screen process, the light intensity information recorded on the composite negative is transferred onto the color matrix to mask it in accordance with the aforementioned color subtraction technique. Other information transfer processes can also be used, such as a cliche-type process for example, the requirement being that the stronger the light intensity recorded at a negative spot, the smaller the resulting mask aperture and the smaller the blackened area of the corresponding matrix color spot.

In a second preferred embodiment of the present invention method, instead of using three masks during the photography steps, only one mask is used, the mask being merely angularly reoriented on the color print each time. For example, for the red color photography step the first mask is used in the exact manner set forth in the hereinabove described first preferred method embodiment, the mask being aligned in registry with the color print to expose print areas in a pattern corresponding to the pattern of the color matrix red spots.

Then, after photographing the so-masked color print through a red-pass filter, the same mask is angularly reoriented to a position where the exposed color print areas would correspond to the blue spots of a matrix the size of the color print, whereupon the masked print is again photographed on the same black and white film frame, this time through the blue-pass filter. Reorientation of the mask to expose print areas in a pattern corresponding to the pattern of the color matrix green spots then facilitates the photographing of the masked matrix through the green-pass filter to thereby complete the triple exposure.

When using the commonly employed spot grouping wherein three circular spots are arranged in the form of an inverted triangle, it is merely necessary to reorient the mask angularly in order to reorient on another spot in each group. To facilitate reorientation of the mask with respect to the color print, the photographic mask can be conveniently mounted in a movable support jig arranged to move the mask in pure angular motion, thereby insuring correct ultimate registry of the composite negative spots with the color matrix spots. Other techniques for photographic masking during the three photographic steps will be apparent to those skilled in the art.

Thus, although the present invention method has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the method of perfonning the various process steps can be utilized without departing from the spirit and scope of the invention as hereinafter claimed.

I claim 1. A method of preparing a matrix mask for a color matrix to be used for the reproduction of images appearing on a color print, said matrix being of the type defining a successive series of identical three color spot groups, each group consisting of a red spot and a blue spot and a green spot, comprising the steps of:

a. photographing on black and white film predetermined areas of said color print defining a pattern of three spot groups corresponding to the spot group pattern of said color matrix, with the light exposure of the film spots corresponding to the matrix red spots being in accordance with the intensity of the red color component at the corresponding areas of said color print, the light exposure of the film spots corresponding to the matrix blue spots being in accordance with the intensity of the blue color component at the corresponding areas of said color print, and the light exposure of the film spots corresponding to the matrix green spots being in accordance with the intensity of the green color component at the corresponding areas of said color print;

b. developing the exposed film to form a negative the size of said color matrix; and,

c. transferring the relative light intensity information from said negative onto a matrix sheet mask in such manner to form apertures therethrough in registry with the pattern spots on said negative, which aperture size being determined by the intensity of the light recorded on the corresponding pattern spot area of the negative.

2. Method according to claim 1, wherein said color print is photographed through a filter which selectively passes only red light to determine the light exposure of the film spots corresponding to the matrix red spots, through a filter which selectively passes only blue light to determine the light exposure of the film spots corresponding to the matrix blue spots, and through a filter which selectively passes only green light to determine the light exposure of the film spots corresponding to the matrix green spots.

3. Method according to claim 2, wherein said color print is photographed three times on the same black and white film frame, one of the exposures being selectively of those color print areas corresponding to the matrix red spots and being made while utilizing the red filter, another of the exposures being selectively of those color print areas corresponding to the matrix blue spots and being made while utilizing the blue filter, and the other of the exposures being selectively of those color print areas corresponding to the matrix green spots and being made while utilizing the green filter.

4. Method according to claim 1, wherein said black and white film is exposed selectively to those color print areas corresponding to the matrix red spots through a filter which selectively passes only red light, to those color print areas corresponding to the matrix blue spots through a filter which selectively passes only blue light, and to those color print areas corresponding to the matrix green spots through a filter which selectively passes only green light.

5. Method according to claim 1, wherein said color print is masked with an opaque sheet mask having a pattern of apertures therethrough defining the predetermined areas of said color print to be photographed.

6. Method according to claim 3, wherein said color print is masked with an opaque sheet mask defining a pattern of apertures corresponding to the matrix red spots while photographing through the red filter, with an opaque sheet mask defining a pattern of apertures corresponding to the matrix blue spots while photographing through the blue filter, and with an opaque sheet mask defining a pattern of apertures corresponding to the matrix green spots while photographing through the green filter.

7. Method according to claim 1, wherein the steps set forth in subparagraph (a) and (b) consist of:

masking said color print with a first opaque mask having a pattern of apertures therethrough corresponding to the pattern of the matrix spots of a first predetermined one of said three colors;

photographing on black and white film the so-masked color print through a filter which selectively passes said first predetermined one of said three colors;

replacing said first opaque mask with a second opaque mask having a pattern of apertures therethrough corresponding to the pattern of the matrix spots of a second predetermined one of said three colors;

photographing the so-called color print through a filter which selectively passes said second predetermined one of said three colors, on the same black and white film frame and with the film in the same alignment with respect to the color print, thereby creating a double exposure of said film frame;

replacing said second opaque mask with a third opaque mask having a pattern of apertures therethrough corresponding to the pattern of the matrix spots of the third predetermined one of said three colors;

photographing the so-masked color print through a filter which selectively passes said third predetermined one of said three colors, on the same black and white film frame and with the film in the same alignment with respect to the color print, thereby creating a triple exposure of said film frame; and,

developing the triple exposed film frame and enlarging the resulting negative to the size of said color matrix.

8. Method according to claim 1, wherein the relative light intensity information is transferred onto said matrix sheet mask by means of a silk-screening process.

9. Method according to claim 7, wherein the relative light intensity information is transferred onto said matrix sheet mask by means of a silk-screening process. 

2. Method according to claim 1, wherein said color print is photographed through a filter which selectively passes only red light to determine the light exposure of the film spots corresponding to the matrix red spots, through a filter which selectively passes only blue light to determine the light exposure of the film spots corresponding to the matrix blue spots, and through a filter which selectively passes only green light to determine the light exposure of the film spots corresponding to the matrix green spots.
 3. Method according to claim 2, wherein said color print is photographed three times on the same black and white film frame, one of the exposures being selectively of those color print areas corresponding to the matrix red spots and being made while utilizing the red filter, another of the exposures being selectively of those color print areas corresponding to the matrix blue spots and being made while utilizing the blue filter, and the other of the exposures being selectively of those color print areas corresponding to the matrix green spots and being made while utilizing the green filter.
 4. Method according to claim 1, wherein said black and white film is exposed selectively to those color print areas corresponding to the matrix red spots through a filter which selectively passes only red light, to those color print areas corresponding to the matrix blue spots through a filter which selectively passes only blue light, and to those color print areas corresponding to the matrix green spots through a filter which selectively passes only green light.
 5. Method according to claim 1, wherein said color print is masked with an opaque sheet mask having a pattern of apertures therethrough defining the predetermined areas of said color print to be photographed.
 6. Method according to claim 3, wherein said color print is masked with an opaque sheet mask defining a pattern of apertures corresponding to the matrix red spots while photographing through the red filter, with an opaque sheet mask defining a pattern of apertures corresponding to the matrix blue spots while photographing through the blue filter, and with an opaque sheet mask defining a pattern of apertures corresponding to the matrix green spots while photographing through the green filter.
 7. Method according to claim 1, wherein the steps set forth in subparagraph (a) and (b) consist of: masking said color print with a first opaque mask having a pattern of apertures therethrough corresponding to the pattern of the matrix spots of a first predetermined one of said three colors; photographing on black and white film the so-masked color print through a filter which selectively passes said first predetermined one of said three colors; replacing said first opaque mask with a second opaque mask having a pattern of apertures therethrough corresponding to the pattern of the matrix spots of a second predetermined one of said three colors; photographing the so-called color print through a filter which selectively passes said second predetermined one of said three colors, on the same black and white film frame and with the film in the same alignment with respect to the color print, thereby creating a double exposure of said film frame; replacing said second opaque mask with a third opaque mask having a pattern of apertures therethrough corresponding to the pattern of the matrix spots of the third predetermined one of said three colors; photographing the so-masked color print through a filter which selectively passes said third predetermined one of said three colors, on the same black and white film frame and with the film in the same alignment with respect to the color print, thereby creating a triple exposure of said film frame; and, developing the triple exposed film frame and enlarging the resulting negative to the size of said color matrix.
 8. Method according to claim 1, wherein the relative light intensity information is transferred onto said matrix sheet mask by means of a silk-screening process.
 9. Method according to claim 7, wherein the relative light intensity information is transferred onto said matrix sheet mask by means of a silk-screening process. 